A spectrometer is a device to measure the wavelength or frequency components of the electromagnetic spectrum. Most optical spectrometers use a diffraction grating or a prism in order to disperse light, where the spectrum of light is separated in space by wavelength. Spectrometers are frequently utilized for environmental or chemical analysis, fluorescence or Raman measurements.
Fresnel zone plates are circular diffraction gratings with radially increasing line density. The radially symmetric rings alternate between opaque and transparent zones. The zones can be spaced so that the diffracted light constructively interferes at the desired focus, creating an image there. Fresnel zone plates behave like a circular lens with focusing behavior which approximates that described by the thin lens formula 1/p+1/q=1/f, where p is the object distance, q is the image distance, and f is the focal length. The main difference between a lens and a zone plate is that the zone plate has different diffraction orders and therefore several focal spots, as opposed to just one focal spot (focal point) for a lens.
In view of the above, it can be an object of the present invention to provide an ultra-compact spectrometer that can fit on a single pixel. Yet another object of the present invention can be to provide an ultra-compact spectrometer that can take advantage of thermal expansion properties of a Fresnel zone plate to provide an indication of a presence of a wavelength, using a single pixel. Still another object of the present invention can be to provide a thermally tunable chip scale, ultra-compact, 20 μm diameter or less spectrometer. Another object of the present invention can be to provide an ultra-compact spectrometer that can be relatively easy to manufacture and that can be used in a cost-effective manner.